Rachel Carson's Nightmare: Herbicide-Tolerant Weeds

October 12, 2012 | 9:57 am
Margaret Mellon
Former contributor

It is ironic that a new scientific paper documenting U.S.agriculture’s mounting dependence on chemical pesticides should appear only weeks after the 50th anniversary of the publication of Rachel Carson’s Silent Spring.

Rachel Carson, author of Silent Spring. Official photo as U.S. Fish and Wildlife Service employee. c. 1940.

One would have hoped that in the five decades since Carson raised the alarm about the overuse of pesticides, society would have made substantial progress on her signature issue. But instead, we are facing a dramatic upsurge in pesticide use.

It’s not that we don’t know how to reduce dependence on pesticides (the term includes both herbicides and insecticides). For a start, we should encourage multiyear crop rotations, cover crops, and enhanced soil quality. If agriculture had been moving along this path for the past 50 years, Silent Spring’s anniversary would be cause for celebration instead of an occasion to gird ourselves for the next big pesticide battle.

Unfortunately, agriculture has doubled down on the large monocultures of crops that make heavy pesticide use inevitable. US commodity farmers now grow only 4 major crops—corn, soybeans, cotton and wheat—and in many parts of the country only two of these. It’s difficult to set up multiyear crop rotations with only two crops.  As a result, the acreages of commodity crops are huge (corn was 93 million acres last year) and farmers often grow the same crop in the same field year after year. Weeds and insects that get hospitable receptions tend to return, forcing farmers to use herbicides and pesticides to beat them back. As long as this structure is in place, farmers will be dependent on pesticides.

One reason conventional agriculture has stayed on the same pesticide-dependent path for so long is the advent of GE (genetic engineering) technology.  Introduced in the early 1990’s, GE’s two major innovations –herbicide-tolerant crops and BT crops–promised to reduce herbicide and insecticide use without major changes in the agriculture system. For a decade or so, the technology delivered on that promise. And while pesticide use was going down, more fundamental reform was set aside.

The Party Is Over: a New Study on Herbicide Use.

A new scientific study by Charles Benbrook of Washington State University shows that biotechnology respite from pesticide use is over.

The Benbrook study, based on analyses of publically available USDA data, documents the trajectory of herbicide use following the introduction of both the herbicide-tolerant (HT) and the BT-toxin containing (BT) crops. I’m going to focus today on the HT crops, by far the major application of GE in crop agriculture, and talk about BT crops later.

The early days of HT crops were heady times for farmers. All of sudden, weeds could be controlled with a single, low dose application of glyphosate, a relatively benign herbicide. Benbrook’s analysis confirms that total herbicide use dipped in each of the first six years after the introduction of HT crops. Farmers were able to replace several applications of older herbicides with a single application of glyphosate (sold commercially as Roundup™). Despite the higher cost of seeds, farmers couldn’t adopt the technology fast enough.

Resistant Weeds: The Cause of Increased Herbicide Use

Because scientists moved the same herbicide resistance genes into three major commodity crops—corn, cotton, soybeans—the use of glyphosate soared.  According to Benbrook, farmers have planted 1.3 billion acres of HT corn, cotton and soybeans in the US since 1996, mostly in HT soybeans.

Because HT crops were so widely used, those few weeds that could withstand glyphosate had a “field day” in the fields.  Slowly but surely, weeds resistant to glyphosate began to infest fields, and farmers had to apply herbicides more often and in higher doses to control them.

The result is that 16 years after introduction, U.S. herbicide use is on the rise. According to Benbrook, US agriculture has used 527 million pounds more herbicides across the three major HT crops—corn, soybeans and cotton—than it would have used without the HT crops.

More Herbicides and More Weeds: The Crisis Ahead

But, this is just the beginning.  Like herbaceous zombies, as long as farmers keep using herbicides, resistant weeds will just keep on coming.

The biotechnology industry’s solution is to engineer crops to resist yet other herbicides to be used along with glyphosate. That means more herbicides use and more super weeds—Rachel Carson’s worst nightmare.

Rather than yet another turn of the pesticide treadmill, we should start now to consider the fundamental changes in agriculture that would discourage weeds in the first place. To learn more, see my colleague Karen Stillerman’s post yesterday.